Nearly any Cree or Rebel LED will give you about the same efficiency, for our purposes for a planted tank. I haven't found a source for Luxeon M's but I haven't really been looking for them either. ...

For those interested, this driver would be perfect for 1 Luxeon M, and it would be FREAKY bright. Enough to light a 10 gallon tank by itself, for low/medium level light. You will have some shadows---...

Speaking from actual experience with a PAR meter and radiometer in hand (a while back), that double 3-watt LED you linked will literally only put out about the same PAR as a single Cree XPG LED. That...

I have a couple of these, they are pretty good. They take anything from 8-40v input, but a few people have had problems using anything over 32v input. 12v, with at least a 700mA capable power supply,...